Gas wells are drilled into subterranean formations to produce natural gas trapped in such formations. Gas wells generally are completed with tubing inside of a wellbore or casing. Regardless of whether the well has a casing, an annular space is provided around the tubing. In many wells, this annular space extends from the formation to the top of the well. In the production of gas, the gas passes from the formation across the annular space and into the tubing. The gas then passes upward through the tubing to a surface conduit.
Often gas passing from the formation to the surface conduit undergoes a reduction in temperature. This temperature reduction may be due to the gas passing through a portion of the well which is at a low temperature. This low temperature may occur where there is a very cold surface temperature and thus a steeply dipping thermal gradient in the upper subterranean formations through which the well passes. This low temperature may also occur where the gas well is on the edge of a mountainous area and melting snow pours cold water through a subterranean formation through which the well passes. The low temperature may also occur as a result of a large pressure reduction in the gas as it passes to the surface, for example, where the gas passes through a downhole pressure regulator.
Upon reduction in temperature of natural gas, when water is present in the gas (wet gas), hydrates are capable of forming. As used herein, the term "wet gas" refers to natural gas containing sufficient moisture to make it susceptible to hydrate formation upon reduction of temperature. Depending upon the pressure of the gas, the hydrates may form at temperatures well above the freezing point of water. Thus, at 1000 pounds per square inch, hydrates may form at a temperature of 61.degree. F. with 0.6 specific gravity gas. These hydrates are crystals, analogous to ice crystals, of water in combination with a liquefiable component of the gas stream. The formation of these hydrates presents a problem in that they can effect a solid blockage to flow of the gas at the points where they form and accumulate. Thus, where the natural gas becomes reduced in temperature in its passage from the formation to the surface conduit, hydrates may form with consequent blockage to the flow of the gas.
Normal production of natural gas from a well frequently involves temporary shutting in of the well. For example, the well may be shut in temporarily for the purpose of avoiding production in excess of state allowables. The problem of the formation of hydrates is particularly severe when production of natural gas is started from a well which has been shut in. The pressure within the shut-in gas well will reach equilibrium with the pressure in the subterranean formation, and this pressure will be higher than the flowing pressure of the well. The pressure drop into the surface conduit on start up will, therefore, be greater than in normal production, engendering greater cooling and thus lower temperatures. Further, the gas will be cooler having attained temperature equilibrium with its environment within the well.
According to this invention, stoppage of gas production from gas wells is prevented by incorporating in the gas a surface active agent which inhibits the formation of gas hydrates and/or the agglomeration of hydrate crystallites into large crystalline masses which are capable of blocking gas flow.
The method of this invention is also applicable to other situations where gas hydrates may affect gas flow, eg. during drilling of gas wells or oil wells where gas is present and in pipelining of gas or gas-containing liquids.